The STS Arms ST4 Improved MOE

By Christopher R. Bartocci

There are many different wonder finishes in the industry today. Some are better than others. Some manufacturers have felt their finish could greatly contribute not only to the corrosion resistance but to the improvement in functioning of their firearm as well. This can be either easier cleaning or no need for oil.

In August of 2010, Vietnam Veteran Ron Downs opened up the doors of STS Arms located in Toledo, Oregon. Downs has decades of shooting experience and in 1911 pistolsmithing. Prior to 2005, Downs’ experience with the AR-15 was solely from the one he carried in the military. The first STS produced rifles left the shop in October of 2010. The first Improved MOE (Magpul Original Equipment) rifle was conceived in 2011 but production did not commence until the end of 2011. The improved models are all marked “ST4.”

STS Arms offers a full line of rifles. They offer basic carbines, MOE carbines, Improved Basic and Improved MOE. In the near future STS plan to reveal their Competition Tactical, Mini-Tactical and Tactical. STS Arms is also very well known to produce complete custom rifles for their customers. This is an excellent service considering most of the top tier manufacturers do not offer custom models as they are geared up for mass production only. Prices will vary considering exactly what the customer wants and the size of their budget. Generally, STS Arms offers 16 inch production barrels. So far custom rifles have been made in 20, 18, 16, 14.5, 11.5, 10.5 and 7.5 inches. To qualified military and law enforcement agencies, STS Arms manufactures selective fire rifles and carbines. STS Arms is also very well known for producing custom 300 Blackout barrels.

STS Arms specializes in Cerakote, which is a ceramic coating manufactured by NIC Industries. There are different types of coatings depending on the part. The Cerakote coating improves the performance and corrosion resistance in firearms. The flexibility of Cerakote offers the customer numerous colors. STS offers Cerakote in black, flat dark earth, olive drab green, foliage green, tactical grey, tungsten grey, patriot brown, orange, hot pink, cobalt black, titanium blue and many camouflage and even red. NIC Industries offers 200+ colors though not all stocked by STS Arms. STS Arms applies Cerakote to all types of firearms ranging from pistols to M2 machine guns. As of this writing, STS Arms just completed applying Cerakote to two M240’s for Troy Industries.

Another finish that is used by STS Arms is Microslick. Microslick is a form of dry film lubricant that is used in the racing industry. These high performance race cars are coating piston skirts, cylinder walls, crank shafts, cam shafts, bearings, gears and valves and other high temperature and high stress components. The finish is designed to reduce friction and to operate without lubricants and allow smooth and consistent cycling of parts while also acting as an anti-seize agent. In firearms, the Microslick ceramic coating increases reliability, reduces galling, reduces heat and friction and allows consistent smooth movement of the bolt and bolt carrier. Microslick creates a permanent bond with metal parts and penetrates a few microns deep and is extremely thin (.25 -.5 mil is the recommended coating thickness) and will have basically no affect on the tolerance of the components. Temperature wise, Microslick can withstand temperatures exceeding 1,200 degrees Fahrenheit, which is around the transformation temperature on a M4 barrel. Microslick has a blue/grey appearance and is an air cured ceramic coating. STS coats the entire bolt carrier group including the firing pin with Microslick as well as the inside of the upper receiver and the inside of the receiver extension. To get the best benefit of Microslick, both surfaces that contact should be coated. All internal parts of STS Arms rifles are coated with NIC Industries Microslick. According to STS Arms, “In our testing of the BCG (bolt carrier group), we started with a dry system and attended several police demos and other demonstrations in the course of a year. The initial test was 1,800 rounds as fast as the officers could reload and shoot it. During the course of more demos, the round count exceeded 3,000 rounds with most of it being full auto. The only failures we experienced on the system were fouling plus time and air moisture changes (caused powder fouling to expand). The failures were only initial loading related. Hand cycling the first round was a little sticky. Firing resulted in no failures. Probably 90 to 95% of rounds fired through the test/demo gun were also suppressed (which is exceedingly dirtier). Other Microslick coated AR platforms have been reported to us to have exceeded 10,000 rounds or more before cleaning was done just to alleviate the crunchy sound of the fouling in the system during shooting and hand cycling (rental guns).”

The rifle supplied for test & evaluation was one of the STS Arms Oregon Special models, which is a limited special occasion model (Ron Downs’ personal demo rifle).

The upper receiver is a standard M4 upper receiver with M4 feed ramps. The inside of the receiver is Microslick finished and the outside is Cerakote H series flat dark earth. The forward assist, charging handle, delta ring and ejection port cover are all Cerakoted as well but in olive green. The Magpul MBus rear sight was mounted on top of the upper receiver.

The barrel is rather unique. STS Arms call this barrel an Improved Barrel Profile and was born of the desire for a non-government profile mid-length gas barrel. The mid-length gas system makes for a more durable and reliable rifle over the standard carbine length gas system. The carbine length gas system creates higher residual pressure upon extraction causing the extractor to work harder and the bolt to take more of a beating due to the higher bolt velocity. The theory of the mid-length system is that it finds that sweet spot between the carbine and rifle length gas system that lowers residual pressure making for an easier extraction and a lower bolt velocity. This both increases reliability and longevity of the rifle’s components. The M5 profile was there merely because the A2 and M4 profile used those diameters under the handguards. STS Arms felt it served no purpose as they felt the meat of the barrel could be redistributed for greater utility. They increased the diameter under the handguards to 0.700 inches and reduced the diameter ahead of the 0.750 inch gas block seat to 0.640 inches. The end result, they said, was the barrel was stiffer where it counted and had less weight up front to further reduce vibration. In recent testing, the barrel retains accuracy a lot longer than an M4 profile barrel when heating up. As far as handling, the barrel is a lot stiffer than a pencil profile barrel, yet is almost indistinguishable from them in the feel of what STS Arms calls “swing weight,” when the shooter is raising/pointing the rifle and when transitioning between targets. STS Arms said after investigation, they determined that salt bath nitride was far superior to chrome lining. Although less expensive than chrome plating, salt bath nitride was fond to be superior in barrel life and accuracy over the hard chrome plated barrel. All barrels are coated with C series Cerakote for high temperatures. Dynamic Arms Development Group, Inc. is the manufacturer of the currents STS Arms improved barrels from 4150 chrome moly vanadium steel. They are button rifled. Standard M4 carbine barrels are produced by various manufacturers and are sourced to STS Arms based on quality and performance. The Improved profile barrels are 1/8 inch twist with 5 lands and grooves. Earlier barrels had a 6 land and groove 1/8. The M4 carbine barrels are the standard 1/7 twist. All Improved barrels are Melonite coated. The rifle was equipped with a Magpul mid-length MOE handguard in olive drab color.

The muzzle device on the T&E rifle was the Primary Weapon Systems FSC556 hider/brake. This is the preferred muzzle brake of STS Arms. However, other muzzle devices are offered if the customer requests something specific.

The lower receiver is manufactured from a 7075 T6 aluminum forging and then coated with a Cerakote H series coating. All exterior components such as selector, bolt catch and mag catch are coated in Cerakote as well. The test and evaluation rifle had all of these components olive drab in color. Due to many of the STS rifles being duty grade weapons, they are standard Mil-Spec trigger groups that are Microslick coated. Some of the custom builds use match triggers including Geissele SSA-E and S3G and Jard non-adjustable models. The rifle received for test and evaluation was a Jard trigger group. As previously stated, the receiver extension had a Microslick coated interior and the exterior was finished in Cerakote in flat dark earth. The stock on the rifle was a Magpul MOE olive drab stock and MOE olive drab pistol grip. The trigger guard was also by Magpul, their enhanced aluminum trigger guard. The KNS anti-rotating hammer and trigger pins were also used on this rifle.

The buffer used was the Enidine AR-restor hydraulic buffer. Although mostly beneficial in fully
automatic weapons as a rate of fire reducer, the hydraulic buffer will slightly dampen recoil on semiautomatic fire. The buffer is also Microslick coated for friction reduction. Along with that the action spring is coated in red Cerakote.

As previously stated, the bolt carrier group was entirely coated in Microslick ceramic coating. That included the firing pin and firing pin retainer. The extractor spring was Cerakote coated in red. There is a black extractor buffer as well. It is a blue gray finish and anti-reflective. The carrier key was staked as per Mil-Spec.

The rifle was equipped with Trijicon ACOG optic for testing. It was a nice day in the Nevada Desert; the Pro Gun Club Range in Boulder City was an excellent place to conduct testing, especially in the hot dry desert environment. The ammunition used was 5.56mm M855 ball. The fit and finish of this rifle was superb. It was clear STS Arms pays very close attention to every detail in the finishing process.

At the same time this rifle arrived, this author received two of the newly imported Hera Arms H3T and H3 polymer magazines manufactured in Germany. These are imported by LAN World, Inc. exclusively. These are new polymer magazines and the H3T has a translucent spine which allows you to see the cartridges. There are two holes in the rear of the translucent material that indicate the 20th and 30th round. The H3 is the same magazine minus the translucent window. Both were black polymer. Fit and finish is excellent. The magazines come with an anti-tilt follower as well.

More than 200 rounds were fired during testing of the rifle. There was no lubricant added. There were no malfunctions with either rifle or magazine. The target was placed at 100 yards on a windy day and the rifle shot from a bench. The rifle shot consistently under 2 MOA. If better ammunition would have been available at this time, I expect the rifle group size would have improved with some 69 or 77gr match ammunition. The rifle certainly exceeds combat accuracy.

Due to the claims made on the Microslick finish, the bolt carrier was removed and examined. Clearly there was carbon and other firing debris all over the carrier group. The bolt carrier group was wiped down with a shop rag. All of the external debris wiped right off, only the small areas where a rag could not reached remained. Then the bolt carrier group was disassembled and again heavy amounts of powder fouling were seen. The firing pin, cam pin and retainer pin were wiped clean. On the bolt, the bolt wiped clean except for the tail where carbon builds up. That had to be scrubbed off with a bronze Otis AP brush. If the rag could reach it, all the fouling came off. There was no notable wear on the bolt carrier group components. The inside of the upper receiver wiped clean easy with a rag as well.

Overall the rifle performed as advertised. This rifle was very impressive in its fit and finish. The receiver was nice and tight and the rifle felt solid. The use of the mid length gas system is a major plus for any carbine length barrel. The use of the Magpul furniture is a enhancement to any rifle system as well. The MOE handguards are far more comfortable than the standard round M4-type handguards plus they can have rail sections added to them easily. The STS Arms rifle is certainly a high end AR built for the serious end user. STS Arms will Cerakote or Microslick any components a customer wants to provide them with as well. So a customer can take their favorite firearm and have it coated with these high speed ceramic finishes. It was most interesting to test the finishing processes. Many manufactures have these wonder finishes and few of them work as advertised. STS Arms makes a high quality arm for the professional as well as the advanced commercial customer. It does not appear as though you will find STS Arms in your local gun shop, they seem to be rather high end that are taken and built custom. STS Arms’ products are in select gun shops, though they are looking for a wider distribution through stocking dealers.

This article first appeared in Small Arms Review V18N2 (April 2014)and was posted online on January 17, 2014